In general, a compressor for a vehicle air conditioner selectively receives power from a power source according to connection/disconnection operations of a clutch, receives refrigerant gas from an evaporator, compresses the refrigerant gas according to a linear reciprocation operation of a piston, and transfers the compressed refrigerant gas to a condenser.
Particularly, variable capacity compressors, which control an inclination angle of a swash plate to vary the discharge capacity thereof, are widely used.
Referring to FIG. 1, a typical variable capacity swash plate type compressor 1 includes: a cylinder block 110 having cylinder bores 112 therein, and including an intake port 114 and an intake muffler chamber 116; a front housing 120 coupled to the front portion of the cylinder block 110, and forming a crank chamber 122 therein; an intake chamber 132 and a discharge chamber 134, which are disposed behind the cylinder block 110; and a rear housing 130 provided with a discharge passage 136.
A valve plate 140, through which refrigerant is introduced and discharged, is disposed between the front housing 120 and the rear housing 130, and has a circular plate shape. The valve plate 140 includes a plurality of refrigerant intake ports 140a and a plurality of refrigerant discharge ports 140b. The refrigerant intake ports 140a are arrayed along an outer circular arc about the front center of the valve plate 140, and the refrigerant discharge ports 140b are arrayed along an inner circular arc about the front center thereof.
An intake reed valve 142 is disposed on the front portion of the valve plate 140, and a discharge reed valve 144 and a retainer 146 are sequentially disposed on the rear portion thereof. A check valve 100 prevents a back flow of the refrigerant to the front side of the valve plate 140.
Further, the swash plate type compressor 1 includes: a driving shaft 160 rotatably disposed in the central portion of the cylinder block 110 and the front housing 120; a swash plate 170 connected through a hinge part 174 to a rotor 172 installed on the driving shaft 160 within the crank chamber 122 wherein an inclination angle of the swash plate 170 is varied according to a pressure variation within the crank chamber 122; and a plurality of pistons 180 connected through a shoe 176 to an edge of the swash plate 170, and reciprocating within the cylinder bores 112 according to a rotation of the swash plate 170 so as to introduce or compress the refrigerant.
A compression coil spring 178 is disposed between the swash plate 170 and the rotor 172 to return the swash plate 170 to the initial position thereof. Thus, the driving shaft 160 and the swash plate 170 integrally rotate so as to discharge the refrigerant compressed within the cylinder block 110, to a condenser through the discharge passage 136, and a discharged amount of the refrigerant is varied according to inclination angles of the swash plate 170.
When an air conditioner of a vehicle is turned off, the swash plate 170 is maintained at a minimum inclination angle, but the minimum inclination angle is not zero. Thus, even when the air conditioner is turned off, a portion of the refrigerant may be discharged from the swash plate type compressor 1 to the condenser. Thus, the check valve 100 is disposed on the rear end of the valve plate 140 in order to prevent refrigerant from being discharged when the air conditioner is turned off, and simultaneously to prevent discharged refrigerant from being returned from the condenser to the swash plate type compressor 1.
Referring to FIGS. 2 to 5, the check valve 100 includes: a valve seat 200 including a refrigerant introduction hole 210 in the central portion thereof; a valve case 300 disposed above the valve seat 200 and including first and second refrigerant discharge holes 310 and 320 along a circumferential surface of a cylindrical body thereof at front and both lateral sides thereof; a spool valve 400 disposed within the valve case 300 to selectively open and close the refrigerant introduction hole 210 and the first and second refrigerant discharge holes 310 and 320; and an elastic member 500 inserted between a support part 330 of the valve case 300 and a stepped part 440 of the spool valve 400.
The first refrigerant discharge hole 310 and a pair of the second refrigerant discharge holes 320 are asymmetrically arrayed along the circumferential surface of the cylindrical body of the valve case 300. Thus, when refrigerant pressure is equal to spring force of the elastic member 500, and the spool valve 400 is vertically moved, the spool valve 400 tightly contacts a wall surface of the valve case 300 provided with the first and second refrigerant discharge holes 310 and 320, and thus, is prevented from moving left and right.
The spool valve 400 includes grooves 420 that longitudinally extend along a circumferential surface of a cylindrical body thereof.
The grooves 420 include a plurality of first grooves 420a and a plurality of second grooves 420b. The first grooves 420a longitudinally extend along the circumferential surface of the cylindrical body of the spool valve 400, and are spaced a constant distance from one another. The second grooves 420b are disposed, respectively, in two pairs of the first grooves 420a facing each other, and extend from a bottom surface of the valve case 300 to introduce the refrigerant, and have a depth greater than that of the first grooves 420a. 
Thus, when the spool valve 400 is initially opened, and the refrigerant is introduced through the refrigerant introduction hole 210, the refrigerant sequentially passes through the second grooves 420b and the first grooves 420a to slowly open the spool valve 400, thereby decreasing valve noise.
However, although the first and second refrigerant discharge holes 310 and 320 are asymmetrically arrayed, and the grooves 420 are configured as described above, when back pressure of the refrigerant exceeds a certain level, the spool valve 400, which would otherwise tightly contact an inner wall of the valve case 300, is spaced apart from the inner wall, and is moved left and right. Thus, the check valve 100 has a limitation in decreasing the valve noise according to back pressure of the refrigerant.